Carbon sorption is the conventional method for treating munitions manufacturing waste containing explosive compounds such as 2,4,6 trinitrotoluene (TNT), trimethylenetrinitronitramine (RDX), and tetramethylenetetranitramine (HMX). The liquid form of this waste is termed “pinkwater.” Typically using granulated activated carbon (GAC) filters, the waste is passed through the GAC with the explosive constituents removed by sorbing onto the carbon. This method is non-destructive, i.e., the sorbed molecules of contaminant remain intact chemically. Thus, the process generates spent contaminant-laden GAC filters that require further treatment, to include regeneration of the carbon filter for re-use or safe disposal at the end of the filter's useful life. The U.S. military and its contractors generate substantial amounts of spent GAC from pinkwater treatment and would save considerable resources by replacing the GAC filtration process with a process that actually destroys or neutralizes energetic contaminants.
Thus, it is a given that conventional sorbing processes have several disadvantages that are immutable. Further, direct oxidation by chemical or biological processes is not as efficient as sequential reduction/oxidation processes due to the relatively oxidized nature of energetics.
It is known to use the Fenton reaction for oxidizing hydrocarbons to their constituents. Typically, the oxidizing agent used in the reaction is hydrogen peroxide, H2O2. Mixed with a metallic salt, H2O2 produces a free radical that breaks the bonds of a hydrocarbon molecule in an exothermic reaction. This results in a low-free-energy state generally associated with the production of carbon dioxide (CO2) and water.
Elemental iron (Fe0) oxidizes to Fe+2 in the presence of oxygen. This removes most of the oxygen from the solution and contributes to the solution attaining an anaerobic state.
Zero-valent iron has been used in permeable reactive barriers (PRBs), an emerging technology that has been applied in recent years to remediate groundwater contaminated with a wide range of pollutants. Permeable Reactive Barrier Technologies for Contaminant Remediation, EPA/600/R-98/125, U.S. EPA, September 1998; Field Applications of In Situ Remediation Technologies: Permeable Reactive Barriers, EPA/542/R-99/002, U.S. EPA, June 1999. Iron is a strong reducing agent (Eo=−0.44V) and can reduce relatively oxidized pollutants, including chlorinated solvents, metals, nitrates, and radionuclides. U.S. EPA (September 1998).
Researchers have shown that iron can reduce TNT, RDX, and HMX at high rates. Hundal, L. S., et al., Removal of TNT and RDX from Water and Soil Using Iron Metal, Environmental Pollution, 97: 55-64, 1997. Further, the Fenton reaction is an established process applied to treat a wide variety of pollutants in hazardous wastes, wastewater, and groundwater. Eckenfelder, W. W., The Role of Chemical Oxidation in Waste Treatment Processes, Proceedings of the First International Symposium on Chemical Oxidation, Technomic Publishing Co., Inc., Lancaster, Pa., pp. 1-10, 1992; Huang, C. P. et al., Advanced Chemical Oxidation: Its Present Role and Potential Future in Hazardous Waste Treatment, Waste Management, 16: 361-377, 1993.
The well-known Fenton reaction has been used in a number of recent patents dealing with environmental remediation. For example, for in-situ subterranean treatment of contaminated ground water or soil, the following employ the Fenton reaction as at least a part of their process: U.S. Pat. No. 6,206,098, In situ Water and Soil Remediation Method and System, to Cooper et al., Mar. 27, 2001 using a catalyst prior to injection of an oxidizer to initiate the Fenton reaction; U.S. Pat. No. 5,967,230, In situ Water and Soil Remediation Method and System, to Cooper et al., Oct. 19, 1999; and U.S. Pat. No. 5,611,642, Remediation Apparatus and Method for Organic Contamination in Soil and Groundwater, to Wilson, Mar. 18, 1997, describing a subterranean system for implementing the Fenton reaction.
U.S. Pat. No. 5,789,649, Method for Remediating Contaminated Soils, to Batchelor, et al., Aug. 4, 1998, describes the use of zero-valent iron and a catalytic metal to degrade chlorinated compound contaminated soil. U.S. Pat. Nos. 5,611,936, 5,616,253, Apr. 1, 1997; and U.S. Pat. No. 5,759,389, Jun. 2, 1998, all entitled Dechlorination of TCE with Palladized Iron, all to Fernando, et al., describe a method to de-chlorinate TCE with elemental iron having a palladium coating.
Zero-valent iron is used for at least part of the remediation process in establishing subterranean permeable reactive barriers as described in U.S. Pat. No. 5,733,067, Method and System for Bioremediation of Contaminated Soil Using Inoculated Support Spheres, to Hunt, et al., Mar. 31, 1998; U.S. Pat. No., 5,833,388, Nov. 10, 1998, and U.S. Pat. No. 5,975,800, Nov. 2, 1999, both entitled Method for Directing Groundwater Flow and Treating Groundwater In Situ, both to Edwards and Dick; U.S. Pat. No. 5,857,810, In Situ Chemical Barrier and Method of Making, to Cantrell and Kaplan Jan. 12, 1999; and U.S. Pat. No. 6,207,114, Reactive Material Placement Technique for Groundwater Treatment, to Quinn, et al., Mar. 27, 2001.
Zero-valent iron powder has been used for in-situ decontamination of halocarbons and metals more noble than iron as described in U.S. Pat. No. 5,975,798, In Situ Decontamination of Subsurface Waste Using Distributed Iron Powder, to Liskowitz et al., Nov. 2, 1999. U.S. Pat. No. 6,132,623, Immobilization of Inorganic Arsenic Species Using Iron, to Nikolaidis, et al., Oct. 17, 2000, describes the use of zero-valent iron to immobilize inorganic arsenic species. U.S. Pat. No. 5,783,088, Method of Removing Oxidized Contaminants from Water, to Amonette, et al., Jul. 21, 1998, describes treatment of oxidized contaminants using a layered aluminosilicate incorporating Fe (II). U.S. Pat. No. 5,538,636, Process for Chemically Oxidizing Highly Concentrated Waste Waters, to Gnann et al., Jul. 23, 1996, uses the Fenton reaction together with electrolysis and multiple steps of neutralization to purify wastewater and address problems associated with the sludge resulting therefrom.